Manual ink proofers of the type disclosed in U.S. Pat. No. 2,990,715 to Bradt dated July 4, 1961 are employed for proofing ink colors in order to accurately predict the results to be obtained by running a selected ink specimen in a printing press.
In flexographic printing, wherein rubber plates are employed for delivering the ink to the stock or paper to be printed, the flexographic ink technician is given an ink specimen which has been determined to be acceptable for use on a particular press, and a production run sample, to be used as the standard for color and density.
One of the most difficult tasks facing a flexographic ink technician is proofing an ink in a manner so that the color will duplicate the color of the production run sample from the flexographic printing press. It is common knowledge to those skilled in the art that if three trained technicians pull a proof, using the same ink on the same hand proofer, three different color shades will result.
Color shade on a flexographic printing press is dependent on the ink film thickness applied to the substrate or stock. The ink film thickness is determined by the speed of the press, the pressure applied between the printing plate and paper; viz., impression, and the pressure between the rollers on the printing unit. Similarly, color shade on a flexographic hand proofer is also dependent on the ink film thickness applied to the substrate which thickness is determined by the speed at which the technician pulls the hand proofer across the substrate, and the impression pressure the technician applies to the proofer while moving it across the substrate. Thus, the speed and impression is totally dependent on the manual skill of the flexographic ink technician, while the only variable not controlled by the technician is the pressure between the ink roller and transfer roller of the manual proofer.
To overcome the disadvantages experienced by manually pulling a proof, the apparatus of the present invention has been devised which comprises, essentially, a fluid motor including a cylinder and piston rod upon which a conventional manual proofer is operatively connected. A valve is provided for controlling the speed at which the piston rod is retracted into the cylinder and concomitantly the proofer on the substrate; and variable pressure means is applied to the proofer to obtain the desired impression pressure. By this construction and arrangement, the speed, impression and roller pressure are completely controlled by the technician, whereby the same ink color will be duplicated each time the apparatus is used.
Each make and model of flexographic presses tend to apply different ink film thicknesses. On any single flexographic press, each print station, sometimes as many as ten, can apply different ink film thicknesses. By calibrating the apparatus of the present invention to a given press and/or unit, the color control problem between ink producer and press can be virtually eliminated.